Process for production of a carboxylic acid/diol mixture suitable for use in polyester production

ABSTRACT

The present invention relates to a process by which a carboxylic acid/diol mixture is obtained from a slurry or cake carboxylic acid product without isolation of a substantially dry carboxylic acid solid. More specifically, the present invention relates to a process by which a terephthalic acid/ethylene glycol mixture suitable as a starting material for polyester or co-polyester production is obtained from a slurry or cake terephthalic acid product without isolation of a substantially dry terephthalic acid solid.

FIELD OF INVENTION

The present invention relates to a process by which a carboxylicacid/diol mixture is obtained from a slurry or cake carboxylic acidproduct without isolation of a substantially dry carboxylic acid solid.More specifically, the present invention relates to a process by which aterephthalic acid/diol mixture suitable as a starting material forpolyester or co-polyester production is obtained from a slurry or caketerephthalic acid product without isolation of a substantially dryterephthalic acid solid.

BACKGROUND OF THE INVENTION

Pursuant to the goal of making polyethylene terephthalate (PET) andother polyesters or co-polyesters, a great deal of patent literature isdedicated to describing the processes for preparing a carboxylicacid/diol mixture suitable as starting material. In general, theseinventions describe specific mixing schemes with a purified terephthalicacid solid and liquid ethylene glycol. Additionally, there issubstantial body of literature devoted to describing the production of apurified terephthalic acid in powder form that is suitable for use inproducing PET and other polyesters or co-polyesters.

The objective of this invention is to describe a process by which thecarboxylic acid/diol mixture suitable as a starting material forpolyester or co-polyester production is obtained from a slurry or cakecarboxylic acid product without isolation of a substantially drycarboxylic acid solid. More specifically, the objective of thisinvention is to describe a process by which a terephthalic acid/diolmixture suitable as a starting material for polyester or co-polyesterproduction is obtained from a slurry or cake terephthalic acid productwithout isolation of a substantially dry terephthalic acid solid.

Usually, purified terephthalic acid solid is produced in a multi-stepprocess wherein a crude terephthalic acid is produced. Liquid phaseoxidation of p-xylene produces crude terephthalic acid. The crudeterephthalic acid does not have sufficient quality for direct use asstarting material in commercial PET. Instead, the crude terephthalicacid is usually refined to purified terephthalic acid solid.

Usually, in terephthalic acid purification processes, the crudeterephthalic acid is dissolved in water and hydrogenated for the purposeof converting 4-carboxybenzaldehyde to p-toluic acid, which is a morewater-soluble derivative, and for the purpose of convertingcharacteristically yellow compounds to colorless derivatives.Significant 4-carboxybenzaldehyde or p-toluic acid in the final purifiedterephthalic acid product is particularly detrimental to polymerizationprocesses as each can act as a chain terminator during the condensationreaction between terephthalic acid and ethylene glycol in the productionof PET. Typical purified terephthalic acid contains on a weight basisless than 25 parts per million (ppm) 4-carboxybenzaldehyde and less than150 ppm p-toluic acid.

A number of other processes have been developed where a terephthalicacid suitable as starting material for commercial PET production isproduced without the use of hydrogenation. Typically, terephthalic acidproduction processes usually involve catalyzed oxidation of p-xylene inan acetic acid solvent followed by filtration and drying of theterephthalic acid.

To produce a terephthalic acid/diol mixture acceptable for PETproduction from a slurry or cake terephthalic acid product poses asubstantially different problem than from a dry terephthalic acidpowder.

Typically, terephthalic acid (TPA) produced via catalyzed oxidation ofp-xylene in an acetic acid solvent produces a slurry or caketerephthalic acid product that contains residual catalyst (e.g cobalt,manganese, and bromine compounds). In a common method of producing asubstantially dry TPA solid from a slurry or cake terephthalic acidproduct, the slurry or cake terephthalic acid product is filtered toseparate a substantial amount of the acetic acid liquid from the TPAsolids. Residual catalyst is usually separated from the slurry or caketerephthalic acid product by washing (rinsing) the wet cake withcatalyst-free acetic acid, water or other solvent. The TPA solid isisolated by drying.

In the present invention, a novel process has been discovered resultingin fewer steps than the currently employed processes. The primaryutility of the invention is reduction of capital and operating costsassociated with the isolation and drying of a terephthalic acid powder.In the conventional approach toward producing terephthalic acid viacatalyzed oxidation of p-xylene in an acetic acid solvent, a slurry orcake terephthalic acid product is filtered, washed, then dried toproduce a terephthalic acid powder suitable as starting material for PETproduction.

In one embodiment of the present invention, the slurry or caketerephthalic acid product is filtered to produce a terephthalic acidcake with solvent and a solvent mother liquor stream. The terephthalicacid cake with solvent is then washed (rinsed) with water to recoverresidual metal catalyst material and to produce a water-wet terephthalicacid cake and a solvent/water by-product liquor. The water-wetterephthalic acid cake is then combined with a diol to produce aterephthalic acid/diol mixture suitable as starting material in acommercial PET process. By eliminating conventional processes forisolating and drying a terephthalic acid solid, the equipment and energynecessary to produce a terephthalic acid powder is also eliminated.

Another surprising and seemingly contradictory aspect of the inventionis the benefit of addition of water to the acetic acid and ethyleneglycol solvents. In general, in conventional processes for producingterephthalic acid, it is necessary to remove water produced in theoxidation process. Typically, use of acetic acid as an oxidation solventnecessitates an additional process step where acetic acid and water areseparated. It is seemingly contradictory to produce an acetic acid andwater mixture when it can be avoided by drying the terephthalic acidfrom the acetic acid solvent.

Additionally, in processes for producing PET via esterification of TPAwith ethylene glycol, water is generated as a reaction by-product. Ingeneral, it is necessary to remove the water produced in theesterification process via an additional process step where ethyleneglycol and water are separated. It is seemingly contradictory to producean ethylene glycol and water mixture when it can be avoided by notintroducing water with the TPA. However, a benefit of this invention isbased on the premise that ethylene glycol/water and acetic acid/waterseparation systems normally exist for conventional TPA and PETproduction processes. In this invention, the value associated witheliminating the TPA drying can be of great benefit when compared totraditional TPA production processes.

SUMMARY OF THE INVENTION

The present invention relates to a process by which a carboxylicacid/diol mixture is obtained from a slurry or cake carboxylic acidproduct without isolation of a substantially dry carboxylic acid solid.More specifically, the present invention relates to a process for theproduction of a terephthalic acid/ethylene glycol mixture suitable asfeedstock for the production of commercial PET. The resulting processcan save energy and has fewer steps than currently employed processes.Specifically, the present invention incorporates a direct displacementof water with ethylene glycol. Incorporation of the displacement stepeliminates the need to isolate a purified terephthalic acid solid andcould eliminate the need for crystallization, solid-liquid separation,drying and solids handling equipment normally found in commercialpurified terephthalic acid processes.

It is an object of this invention to provide a process for producing acarboxylic acid/diol mixture from a slurry or cake carboxylic acidproduct without isolation of a substantially dry carboxylic acid solid.

It is an object of this invention to provide a process for producing acarboxylic acid/diol mixture from a slurry or cake carboxylic acidproduct suitable as starting material for the production of polyestersor co-polyesters without isolation of a substantially dry carboxylicacid solid.

It is another object of this invention to provide a process forproducing a terephthalic acid/diol mixture from a slurry or caketerephthalic acid product without isolation of a substantially dryterephthalic acid solid.

It is another object of this invention to provide a process forproducing a terephthalic acid/ethylene glycol mixture from aterephthalic acid solvent slurry or cake without isolation of asubstantially dry terephthalic acid solid.

It is another object of this invention to provide a process forproducing a terephthalic acid/ethylene glycol mixture without isolationof a substantially dry terephthalic acid solid by removing water from awater-wet terephthalic acid cake through the use of a carboxylicacid/diol mixing zone.

In a first embodiment of this invention, a process for producing acarboxylic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a liquor exchange zone impurities from a        carboxylic acid slurry to form a water-wet carboxylic acid cake,        a mother liquor stream, a solvent mother liquor stream, and a        solvent/water byproduct liquor stream;    -   (b) routing the water-wet carboxylic acid cake to a vapor seal        zone; and    -   (c) adding at least one diol to the water-wet carboxylic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the carboxylic acid/diol mixture.

In another embodiment of this invention, a process for producing acarboxylic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a solvent liquor exchange zone impurities from a        carboxylic acid slurry to form a carboxylic acid cake with        solvent, a mother liquor stream, and a solvent mother liquor        stream;    -   (b) adding water in a water wash zone to the carboxylic cake        with solvent to produce a water-wet carboxylic acid cake and a        solvent/water by product liquor stream;    -   (c) routing the water-wet carboxylic acid cake to a vapor seal        zone; and    -   (d) adding at least one diol to the water-wet carboxylic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the carboxylic acid/diol mixture.

In another embodiment of this invention, a process for producing acarboxylic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a solid-liquid separation zone impurities from a        carboxylic acid slurry to form a slurry or cake carboxylic acid        product and a mother liquor stream;    -   (b) removing in a solvent-water liquor exchange zone impurities        from the slurry or cake carboxylic acid product to form a        water-wet carboxylic acid cake, a solvent mother liquor stream,        and a solvent/water byproduct liquor stream;    -   (c) routing the water-wet carboxylic acid cake to a vapor seal        zone; and    -   (d) adding at least one diol to the water-wet carboxylic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the carboxylic acid/diol mixture.

In another embodiment of this invention, a process for producing acarboxylic acid/diol mixture is provided, the process comprises:

-   -   (a) removing a solvent from a slurry or cake carboxylic acid        product in a solvent-water liquor exchange zone; wherein a        substantial portion of the solvent in the slurry or cake        carboxylic acid product is replaced with water to form a        water-wet carboxylic acid cake;    -   (b) routing the water-wet carboxylic acid cake to a vapor seal        zone; and    -   (c) adding at least one diol to the water-wet carboxylic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the carboxylic acid/diol mixture.

In another embodiment of this invention, a process for producing aterephthalic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a solvent wash zone impurities from a slurry or        cake terephthalic acid product to form a terephthalic acid cake        with acetic acid;    -   (b) removing a substantial portion of a solvent in a water wash        zone from the terephthalic acid cake with acetic acid to form a        water-wet terephthalic acid cake; and    -   (c) routing the water-wet terephthalic acid cake to a vapor seal        zone; and    -   (d) adding at least one diol to the water-wet terephthalic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the terephthalic acid/diol mixture.

In another embodiment of this invention, a process for producing aterephthalic acid/diol mixture is provided, the process comprises:

-   -   (a) removing a solvent from a slurry or cake terephthalic acid        product in a solvent liquor exchange zone; wherein a substantial        portion of the solvent in the slurry or cake terephthalic acid        product is replaced with water to form a water-wet terephthalic        acid cake;    -   (b) routing the water-wet terephthalic acid cake to a vapor seal        zone; and    -   (c) adding at least one diol to the water-wet terephthalic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the terephthalic acid/diol mixture.

In another embodiment of this invention, a process for producing aterephthalic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a solvent wash zone impurities from a slurry or        cake terephthalic acid product from a terephthalic acid cake        with acetic acid; wherein the solvent wash zone comprises at        least one solid-liquid separation device that is operated at a        temperature between about 40° C. to about 155° C.;    -   (b) removing a substantial portion of a solvent in a water wash        zone from the terephthalic acid cake with acetic acid to form a        water-wet terephthalic acid cake; wherein the water wash zone        comprises at least one solid-liquid separation device that is        operated at a temperature between about 40° C. to about 155° C.;    -   (c) adding at least one diol to the water-wet terephthalic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the terephthalic acid/diol mixture; wherein        the adding occurs at a temperature between about 40° C. to about        290° C.; wherein the diol is ethylene glycol.

In another embodiment of this invention, a process for producing acarboxylic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a solid-liquid separation zone impurities from a        carboxylic acid slurry to form a slurry or cake carboxylic acid        product and a mother liquor stream;    -   (b) adding solvent to a slurry or cake carboxylic acid product        in a solvent wash zone to the slurry or cake carboxylic acid        product to produce a carboxylic acid cake with solvent and a        solvent mother liquor stream;    -   (c) adding water in a water wash zone to the carboxylic cake        with solvent to produce a water-wet carboxylic acid cake and a        solvent/water by product liquor stream;    -   (d) routing the water-wet carboxylic acid cake to a vapor seal        zone; and    -   (e) adding at least one diol to the water-wet carboxylic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the carboxylic acid/diol mixture.

In another embodiment of this invention, a process for producing aterephthalic acid/diol mixture is provided, the process comprises:

-   -   (a) removing in a solid-liquid separation zone impurities from a        crude terephthalic acid slurry to form a slurry or cake        terephthalic acid product and a mother liquor stream;    -   (b) adding solvent in a solvent wash zone to the slurry or cake        terephthalic acid product to produce a terephthalic acid cake        with solvent and a solvent mother liquor stream;    -   (c) adding water in a water wash zone to the terephthalic acid        cake with solvent to produce a water-wet terephthalic acid cake        and a solvent/water by product liquor stream;    -   (d) routing the water-wet terephthalic acid cake to a vapor seal        zone; and    -   (e) adding at least one diol to the water-wet terephthalic acid        cake in a carboxylic acid/diol mixing zone to remove a portion        of the water to form the terephthalic acid/diol mixture.

These objects, and other objects, will become more apparent to otherswith ordinary skill in the art after reading this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of this invention, a process forproducing a carboxylic acid/diol mixture.

FIG. 2 illustrates another embodiment of this invention, a process forproducing a carboxylic acid/diol mixture by utilizing a liquor exchangezone.

FIG. 3 illustrates another embodiment of this invention, a process forproducing a carboxylic acid/diol mixture by utilizing a solvent-waterliquor exchange zone.

FIG. 4 illustrates another embodiment of this invention, a process forproducing a carboxylic acid/diol mixture by utilizing a solvent liquorexchange zone.

DESCRIPTION OF THE INVENTION

In an embodiment of this invention shown in FIG. 1, a process forproducing a carboxylic acid/diol mixture 200 is provided. The processcomprises:

Step (a) comprises optionally removing impurities from a carboxylic acidslurry 30 in an solid-liquid displacement zone 40 to form a slurry orcake carboxylic acid product 70 and a mother liquor stream 60;

The carboxylic acid slurry comprises 30 at least one carboxylic acid,catalyst, at least one solvent, and impurities. The impurities typicallycomprise at least one or more of the following compounds:4-carboxybenzaldehyde(4-CBA), trimellitic acid(TMA), and2,6-dicarboxyfluorenone(2,6-DCF). Suitable solvents include, but are notlimited to, aliphatic mono-carboxylic acids, preferably containing 2 to6 carbon atoms, or benzoic acid and mixtures thereof and mixtures ofthese compounds with water. Preferably the solvent is acetic acid mixedwith water, in a ratio of about 5:1 to about 99:1, preferably betweenabout 8:1 and about 49:1. Throughout the specification acetic acid willbe referred to as the solvent. However, it should be appreciated thatother suitable solvents, such as those disclosed previously, may also beutilized. The solvent typically comprises acetic acid, but can be anysolvent that has been previously mentioned.

The carboxylic acid slurry 30 can be produced by oxidizing in aoxidation zone an aromatic feed stock. In one embodiment, the aromaticfeedstock comprises paraxylene. The oxidation zone comprises at leastone oxidation reactor, and the carboxylic acid slurry comprises at leastone carboxylic acid. The oxidation reactor can be operated attemperatures between about 120° C. and about 250° C., preferably about140° C. to about 170° C. Typically the aromatic feed stock comprisesparaxylene and the carboxylic acid comprises terephthalic acid. In oneembodiment of the invention the oxidation zone comprises a bubblecolumn.

Therefore, for example, when terephthalic acid is utilized, thecarboxylic acid slurry 30 would be referred to as terephthalic acidslurry and the carboxylic acid/diol mixture 200 would be referred to asa terephthalic acid/diol mixture.

Carboxylic acids include any carboxylic acid produced via controlledoxidation of an organic precursor compound. For example carboxylic acidsinclude aromatic dicarboxylic acids preferably having 8 to 14 carbonatoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbonatoms, or cycloaliphatic dicarboxylic acids preferably having 8 to 12carbon atoms. Other examples of suitable carboxylic acids include, butare not limited to, terephthalic acid, benzoic, p-toulic, isophthalicacid, trimellitic acid, naphthalene dicarboxylic acid,cyclohexanedicarboxylic acid, cyclohexanediacetic acid,diphenyl-4,4′-dicarboxylic acid, diphenyl-3,4′-dicarboxylic acid,2,2,-dimethyl-1,3-propandiol dicarboxylic acid, succinic acid, glutaricacid, adipic acid, azelaic acid, sebacic acid, and mixtures thereof.

Terephthalic acid slurry is conventionally synthesized via the liquidphase oxidation of paraxylene in the presence of suitable oxidationcatalyst. Suitable catalysts include, but are not limited to, cobalt,manganese and bromine compounds, which are soluble in the selectedsolvent. In one embodiment of the invention the catalyst comprisescobalt, bromine and manganese. The cobalt and manganese combined can bein concentrations of about 100 ppm to about 2700 ppm by weight in theliquor. The bromine can be in concentrations of about 1000 ppm to about2500 ppm by weight in the liquor.

The carboxylic acid slurry 30 is fed to a solid-liquid displacement zone40 capable of removing a portion of the liquid contained in thecarboxylic acid slurry 30 to produce a slurry or cake carboxylic acidproduct in conduit 70. The removal of a portion of the liquid to producea slurry or cake carboxylic acid product in conduit 70 can beaccomplished by any means known in the art. A portion means at least 5%by weight of the liquid is removed. Typically, the solid-liquiddisplacement zone 40 comprises a solid-liquid separator that is selectedfrom the group consisting of a decanter centrifuge, rotary diskcentrifuge, belt filter, rotary vacuum filter, and the like. Thecarboxylic acid slurry in conduit 30 is fed to the solid-liquiddisplacement zone 40 comprising at least one solid-liquid separator. Thesolid-liquid separator(s) can be operated at temperatures between about50° C. to about 200° C., preferably 140° C. to about 170° C. Thesolid-liquid separator(s) can be operated at pressures between about 0psig to about 200 psig. The solid-liquid separator in the solid-liquiddisplacement zone 40 may be operated in continuous or batch mode,although it will be appreciated that for commercial processes, thecontinuous mode is preferred.

The impurities are displaced from the solid-liquid displacement zone 40into a mother liquor stream and withdrawn via line 60. In one embodimentof the invention, additional solvent is fed to the solid-liquiddisplacement zone 40 via line 50 to reslurry the carboxylic acid slurry30 and form a slurry or cake carboxylic acid product 70. When aterephthalic acid slurry is utilized in the solid-liquid separation zone40, a slurry or cake terephthalic acid product is produced. The slurryor cake terephthalic acid product typically comprises terephthalic acidand acetic acid. The mother liquor 60 is withdrawn from solid-liquiddisplacement zone 40 via line 60 and comprises a solvent, typicallyacetic acid, catalyst, and bromine compounds. The mother liquor in line60 may either be sent to a process for separating impurities fromoxidation solvent via lines not shown or recycled to the catalyst systemvia lines not shown. One technique for impurity removal from the motherliquor 60 commonly used in the chemical processing industry is to drawout or “purge” some portion of the recycle stream. Typically, the purgestream is simply disposed of or, if economically justified, subjected tovarious treatments to remove undesired impurities while recoveringvaluable components. Examples of impurity removal processes include U.S.Pat. No. 4,939,297 and U.S. Pat. No. 4,356,319, herein incorporated byreference.

Step (b) comprises removing in a solvent wash zone 80 residualimpurities from a slurry or cake carboxylic acid product 70 to form acarboxylic acid cake with solvent 110 and a solvent mother liquor stream100.

Conduit 70 contains a slurry or cake carboxylic acid product 70comprising a carboxylic acid, residual impurities and a solvent. Theresidual impurities comprise residual catalyst (typically but notlimited to cobalt, manganese, or bromine). Suitable solvents include,but are not limited to, aliphatic mono-carboxylic acids, preferablycontaining 2 to 6 carbon atoms, or benzoic acid and mixtures thereof andmixtures of these compounds with water. Preferably, the solvent iscomprised of mainly acetic acid and/or some water. The ratio of aceticacid to water can range from 50:50 to 98:2 acetic acid to water by mass,more preferably in the range of 85:15 to 95:5, and most preferably inthe range of 90:10 to 97:3. Suitable carboxylic acids include by are notlimited to terephthalic acid, isophthalic acid, naphthalene dicarboxylicacid, trimellitic acid, and mixtures thereof.

The slurry or cake carboxylic acid product 70 is in the range of 10-90%by weight carboxylic acid. Preferably the slurry or cake carboxylic acidproduct 70 is in the range of 25-40% by weight carboxylic acid for aslurry and in the range of 70-90% by weight for the cake product. Mostpreferably, the slurry or cake carboxylic acid product 70 is in therange of 30-40% by weight carboxylic acid. The slurry or cake carboxylicacid product in conduit 70 is then introduced into a solvent wash zone80, wherein a substantial portion of solvent is recovered in the solventmother liquor stream in conduit 100. The solvent mother liquor 102comprises a substantial portion of the solvent. In one embodiment of theinvention, additional solvent can be added via conduit 90 countercurrent to the flow of the slurry or cake carboxylic acid product 70 inthe solvent wash zone 80. The amount of stages of solvent countercurrent wash can be any amount of stages necessary to produce thecarboxylic cake with solvent to the desired purity. Typically, theamount of stages in the solvent counter current wash can be about 1 toabout 8, preferably about 2 to about 6, most preferably about 2 to about4. For wash with more than one stage, counter current flow ispreferable. Solvent counter current wash is preferable because typicallyit results in less solvent being used as compared to a process whensolvent counter current wash is not utilized.

The solvent wash zone 80 comprises at least one solid-liquid separationdevice capable of efficiently separating solids and liquids. Thesolid-liquid separation device can typically be comprised of, but notlimited to, the following types of devices: centrifuges, cyclones,rotary drum filters, belt filters, press filters, etc. The solvent washzone 80 comprises at least one solid-liquid separation device(s) 110which can operate within a temperature range of from approximately 40°C. to 155° C. Preferably the solid-liquid separation device(s) 110 canoperate within a temperature range of from about 80° C. to about 150° C.Most preferably the solid-liquid separation device(s) 110 can operatewithin a temperature range of from about 90° C. to about 150° C. Acarboxylic acid cake with solvent 110, is produced wherein the moisturecomposition of the carboxylic acid cake with solvent 110 can be in therange of 0.5-30% by weight moisture, preferably in the range of 1-20%moisture, most preferably in the range of 1-10% moisture. Optionally,the residual solvent can be removed by a gas displacement step tominimize solvent contamination with wash. When the carboxylic acid isterephthalic acid and the solvent is acetic acid a terephthalic acidcake with acetic acid is produced.

Step (c) comprises optionally removing a substantial portion of asolvent in a water wash zone 120 from the carboxylic acid cake withsolvent 110 to form a water-wet carboxylic acid cake 100 and asolvent/water byproduct liquor stream 140.

The carboxylic acid cake with solvent 110, is then subjected to a washor “rinsing” with water or substantially water with residual amounts ofsolvent in the water wash zone 120, wherein a substantial portion of thesolvent is replaced with water to form a water-wet carboxylic acid cake150. The water-wet carboxylic acid cake 150, is preferably in the rangeof about 0.5% to about 30% moisture, more preferably in the range ofabout 1 to about 20% moisture, and most preferably in the range of about1% to about 10% moisture. The residual moisture of the water-wetcarboxylic acid cake 150, should contain less than about 2% solvent on amass basis. Additionally, the water-wet carboxylic acid cake 150 shouldcontain less than 1% of any metals, preferably less than 100 ppm byweight, most preferably less than 10 ppm by weight, typically used ascatalysts in p-xylene oxidation, in the slurry or cake carboxylic acidproduct in conduit 70, should remain in the water-wet carboxylic acidcake 150. Examples of metals include but are not limited to cobalt, andmanganese.

Wash water is introduced into the water wash zone 120 via conduit 130.The wash water should be, on a continuous basis, comprise a mass feedrate in ratio with the solids in the carboxylic cake with solvent 110 inthe range of about 0.1:1 to about 1.5:1, preferably in the range ofabout 0.1:1 to about 0.6:1, most preferably in the range of about 0.2:1to about 0.4:1. There are no limitations on the temperature or pressureof the wash water including the use of vaporized water, steam, or acombination of water and steam, as wash. In one embodiment of theinvention, wash water is introduced counter current to the carboxylicacid cake with solvent.

Additional wash water can be added via conduit 130 counter current tothe flow of the carboxylic acid cake with solvent 110 in the water washzone 120. The amount of stages of water counter current wash can be anyamount of stages necessary to produce the water wet carboxylic acid caketo the desired purity. Typically, the amount of stages in the watercounter current wash can be about 1 to about 8, preferably about 2 toabout 6, most preferably about 2 to about 4. For wash with more than onestage, counter current flow is preferable. Water counter current wash ispreferable because typically it results in less water being used ascompared to a process when water counter current wash is not utilized.

The water wash zone comprises a solid-liquid separation device 120 cantypically be comprised of, but not limited to, the following types ofdevices: centrifuges, cyclones, rotary drum filters, belt filters, pressfilters, etc. The solid-liquid separation device can be operated withina temperature range of from about 40° C. to about 155° C. Preferably,the second solid-liquid separation device can operate within atemperature range of from about 80° C. to about 150° C. Most preferably,the second solid-liquid separation device can operate within atemperature range of from about 90° C. to about 150° C.

Optionally, the solvent/water byproduct liquor from the water wash zone120, is segregated from the solvent mother liquor stream produce by thesolvent wash zone 80.

Step (d) comprises routing the water-wet carboxylic acid cake 150 to avapor seal zone 160.

The water-wet carboxylic acid cake 150 is passed through a vapor sealzone 160 comprising a vapor seal device, and exits the vapor seal devicevia conduit 170. The vapor seal device allows the water-wet carboxylicacid cake 150 to exit the counter current wash zone 120 but preventsdiol from the carboxylic acid/diol mixing zone 180 from entering thecounter current wash zone or any process zone proceeding the vapor sealzone 160. The vapor seal device can be any device known in the art.Examples include, but are not limited to rotary air lock valve, andsolid conveying extruders.

Step (e) comprises adding at least one diol 190 to the water-wetcarboxylic acid cake 170 in a carboxylic acid/diol mixing zone 180 toremove a portion from the water-wet carboxylic acid cake 170 of thewater to form the carboxylic acid/diol mixture 200.

Finally, the water-wet carboxylic acid cake 170, which is nowsubstantially free of solvent is combined with a diol 190 in acarboxylic acid mixing zone 180, to form a carboxylic acid/diol mixture200 suitable for PET production and other polyesters or co-polyesters.There are no special limitations on the carboxylic acid/diol mixing zone180 with the exception that it comprises a device that must provideintimate contact between the water-wet carboxylic acid cake 170, and thediol 190 to produce a the carboxylic acid/diol mixture 200. Examples ofsuch devices include, but are not limited to the following: an agitatedvessel, static mixer, screw conveyor, PET esterification reactor(s),etc. A solid eductor could be used to introduce the water-wet carboxylicacid cake into the device. Nor is there any specific limitation on thetemperature range at which the device can operate. However, it ispreferable that the temperature of device does not exceed approximately280° C., temperatures normally found within PET esterification reactors.

At least one diol in conduit 190 can be introduced in such a manner asto optionally displace the water as the dominant slurrying liquid. Thiscan be accomplished by introducing a diol via conduit 190 as a saturatedliquid at a temperature which is sufficient to vaporize the water. Inone embodiment of the invention, the diol in conduit 190 is introducedas a saturated or superheated vapor. The diol in conduit 190 is at leastone selected from the group consisting of ethylene glycol, diethyleneglycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, thediol in conduit 190 is ethylene glycol. Note that within the systemshown in FIG. 1, a substantially dry carboxylic acid solid is notformed. The primary advantage in not forming a carboxylic acid dry solidis the elimination of solids handling equipment. Examples of solidshanding equipment include but are not limited to a dryer, conveysystems, and silos.

In other embodiments of this invention step (a), step (b) and step (c)can be combined into one zone known as the liquor exchange zone 250 asshown in FIG. 2. The liquor exchange zone 250 comprises at least onesolid-liquid separation device capable of performing the combinedfunction of the solid-liquid separation zone 40, the solvent wash zone80 and the water wash zone 120 as previously described. Step (b) andstep (c) can also be combined into one zone known as the solvent-waterliquor exchange zone 260 as shown in FIG. 3. Finally step (a) and step(b) can be combined into one zone known as the solvent liquor exchangezone 270 as show in FIG. 4. In each of the above embodiments comprisesat least one solid-liquid separation device capable of performing thefunctions of the combined zones as previously described. Examples ofdevices that can be used in the liquor exchange zone 250, or thesolvent-water liquor exchange zone 260, or the solvent liquor exchangezone 270 included but are not limited to, the following type of devicescentrifuges, cyclones, filters, and such or combination thereof.

1. A process for producing a carboxylic acid/diol mixture, said processcomprising: (a) removing in a liquor exchange zone impurities from acarboxylic acid slurry to form a water-wet carboxylic acid cake, amother liquor stream, a solvent mother liquor stream, and asolvent/water byproduct liquor stream; (b) routing said water-wetcarboxylic acid cake to a vapor seal zone; and (c) adding at least onediol to said water-wet carboxylic acid cake in a carboxylic acid/diolmixing zone to form said carboxylic acid/diol mixture.
 2. A processaccording to claim 1 wherein said carboxylic acid is selected from agroup consisting of terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, trimellitic acid, and mixtures thereof.
 3. A processaccording to claim 1 or 2 wherein said diol is selected from the groupconsisting of ethylene glycol, diethylene glycol, n-butylene glycol,i-butylene glycol, n-propylene glycol, 1,4 butanediol,cyclohexanedimethanol, and mixtures thereof.
 4. A process according toclaim 1 wherein said carboxylic acid/diol mixing zone comprises at leastone device selected from the group consisting of an agitated vessel, astatic mixer, a screw conveyor, and a PET esterification reactor.
 5. Aprocess according to claim 1 wherein said carboxylic acid isterephthalic acid and said diol is ethylene glycol.
 6. A process forproducing a carboxylic acid/diol mixture, said process comprising: (a)removing in a solvent liquor exchange zone impurities from a carboxylicacid slurry to form a carboxylic acid cake with solvent, a mother liquorstream, and a solvent mother liquor stream; (b) adding water in a waterwash zone to said carboxylic cake with solvent to produce a water-wetcarboxylic acid cake and a solvent/water by product liquor stream; (c)routing said water-wet carboxylic acid cake to a vapor seal zone; and(d) adding at least one diol to said water-wet carboxylic acid cake in acarboxylic acid/diol mixing zone to form said carboxylic acid/diolmixture.
 7. A process according to claim 6 wherein said carboxylic acidis selected from a group consisting of terephthalic acid, isophthalicacid, naphthalene dicarboxylic acid, trimellitic acid and mixturesthereof.
 8. A process according to claim 6 or 7 wherein said diol isselected from the group consisting of ethylene glycol, diethyleneglycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4butanediol, cyclohexanedimethanol, and mixtures thereof.
 9. A processaccording to claim 6 wherein said carboxylic acid/diol mixing zonecomprises at least one device selected from the group consisting of anagitated vessel, a static mixer, a screw conveyor, and a PETesterification reactor.
 10. A process according to claim 6 wherein saidcarboxylic acid is terephthalic acid and said diol is ethylene glycol.11. A process for producing a carboxylic acid/diol mixture, said processcomprising: (a) removing in a solid-liquid separation zone impuritiesfrom a carboxylic acid slurry to form a slurry or cake carboxylic acidproduct and a mother liquor stream; (b) removing in a solvent-waterliquor exchange zone residual impurities from said slurry or cakecarboxylic acid product to form a water-wet carboxylic acid cake, asolvent mother liquor stream, and a solventwater byproduct liquorstream; (c) routing said water-wet carboxylic acid cake to a vapor sealzone; and (d) adding at least one diol to said water-wet carboxylic acidcake in a carboxylic acid/diol mixing zone to form said carboxylicacid/diol mixture.
 12. A process according to claim 11 wherein saidcarboxylic acid is selected from a group consisting of terephthalicacid, isophthalic acid, naphthalene dicarboxylic acid, trimellitic acidand mixtures thereof.
 13. A process according to claim 11 or 12 whereinsaid diol is selected from the group consisting of ethylene glycol,diethylene glycol, n-butylene glycol, i-butylene glycol, n-propyleneglycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. 14.A process according to claim 11 wherein said carboxylic acid/diol mixingzone comprises at least one device selected from the group consisting ofan agitated vessel, a static mixer, a screw conveyor, and a PETesterification reactor.
 15. A process according to claim 11 wherein saidcarboxylic acid is terephthalic acid and said diol is ethylene glycol.16. A process for producing a carboxylic acid/diol mixture, said processcomprising the following steps: (a) removing a solvent from a slurry orcake carboxylic acid product in a solvent-water liquor exchange zone;wherein a substantial portion of the solvent in said slurry or cakecarboxylic acid product is replaced with water to form a water-wetcarboxylic acid cake; (b) routing said water-wet carboxylic acid cake toa vapor seal zone; and (c) adding at least one diol to said water-wetcarboxylic acid cake in a carboxylic acid/diol mixing zone to form saidcarboxylic acid/diol mixture.
 17. A process according to claim 16wherein said carboxylic acid is selected from a group consisting ofterephthalic acid, isophthalic acid, naphthalene dicarboxylic acid,trimellitic and mixtures thereof.
 18. A process according to claim 16 or17 wherein said diol is selected from the group consisting of ethyleneglycol, diethylene glycol, n-butylene glycol, i-butylene glycol,n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixturesthereof.
 19. A process according to claim 16 wherein said carboxylicacid/diol mixing zone comprises at least one device selected from thegroup consisting of an agitated vessel, a static mixer, a screwconveyor, and a PET esterification reactor.
 20. A process for producinga terephthalic acid/diol mixture, said process comprising: (a) removingin a solvent wash zone residual impurities from a slurry or caketerephthalic acid product to form a terephthalic acid cake with aceticacid; (b) removing a substantial portion of a solvent in a water washzone from said terephthalic acid cake with acetic acid to form awater-wet terephthalic acid cake; and (c) routing said water-wetterephthalic acid cake to a vapor seal zone; and (d) adding at least onediol to said water-wet terephthalic acid cake in a carboxylic acid/diolmixing zone to form said terephthalic acid/diol mixture.
 21. A processaccording to claim 20 wherein said solvent wash zone comprises asolid-liquid separation device that is operated at a temperature betweenabout 40° C. to about 155° C.
 22. A process according to claim 21wherein said water wash zone comprises a solid-liquid separation devicethat is operated at a temperature between about 40° C. to about 155° C.23. A process according to claim 20 or 21 wherein said adding occurs ata temperature between about 40° C. to about 290° C.
 24. A processaccording to claim 20 wherein said diol is selected from the groupconsisting of ethylene glycol, diethylene glycol, n-butylene glycol,i-butylene glycol, n-propylene glycol, 1,4 butanediol,cyclohexanedimethanol, and mixtures thereof.
 25. A process according toclaim 20 wherein said diol is ethylene glycol.
 26. A process accordingto claim 20 wherein said carboxylic acid/diol mixing zone comprises adevice selected from the group consisting of an agitated vessel, astatic mixer, a screw conveyor, and a PET esterification reactor.
 27. Aprocess for producing a terephthalic acid/diol mixture, said processcomprising: (a) removing a solvent from a slurry or cake terephthalicacid product in a solvent-water liquor exchange zone; wherein asubstantial portion of the solvent in said slurry or cake terephthalicacid product is replaced with water to form a water-wet terephthalicacid cake; (b) routing said water-wet terephthalic acid cake to a vaporseal zone; and (c) adding at least one diol to said water-wetterephthalic acid cake in a carboxylic acid/diol mixing zone to formsaid terephthalic acid/diol mixture.
 28. A process according to claim 27wherein said solvent liquor exchange zone comprises a solid-liquidseparation device that is operated at a temperature between about 40° C.to about 155° C.
 29. A process according to claim 27 wherein said addingoccurs at a temperature between about 40° C. and 290° C.
 30. A processaccording to claim 27 wherein said diol is selected from the groupconsisting of ethylene glycol, diethylene glycol, n-butylene glycol,i-butylene glycol, n-propylene glycol, 1,4 butanediol,cyclohexanedimethanol, and mixtures thereof.
 31. A process according toclaim 27 wherein said diol is ethylene glycol.
 32. A process accordingto claim 27 wherein said carboxylic acid/diol mixing zone comprises adevice selected from the group consisting of an agitated vessel, astatic mixer, a screw conveyor, and a PET esterification reactor.
 33. Aprocess for producing a terephthalic acid/diol mixture, said processcomprising: (a) removing in a solvent wash zone residual impurities froma slurry or cake terephthalic acid product from a terephthalic acid cakewith acetic acid; wherein said solvent wash zone comprises at least onesolid-liquid separation device that is operated at a temperature betweenabout 40° C. to about 155° C.; (b) removing a substantial portion of asolvent in a water wash zone from said terephthalic acid cake withacetic acid to form a water-wet terephthalic acid cake; wherein saidwater wash zone comprises at least one solid-liquid separation devicethat is operated at a temperature between about 40° C. to about 155° C.;(c) routing said water-wet terephthalic acid cake to a vapor seal zone;and (d) adding at least one diol to said water-wet terephthalic acidcake in a carboxylic acid/diol mixing zone to form said terephthalicacid/diol mixture; wherein said adding occurs at a temperature betweenabout 40° C. to about 290° C.; wherein said diol is ethylene glycol. 34.A process for producing a carboxylic acid/diol mixture, said processcomprising: (a) removing in a solid-liquid separation zone impuritiesfrom a carboxylic acid slurry to form a slurry or cake carboxylic acidproduct and a mother liquor stream; (b) adding solvent to a slurry orcake carboxylic acid product in a solvent wash zone to said slurry orcake carboxylic acid product to produce a carboxylic acid cake withsolvent and a solvent mother liquor stream; (c) optionally, adding waterin a water wash zone to said carboxylic cake with solvent to produce awater-wet carboxylic acid cake and a solvent/water by product liquorstream; (d) routing said water-wet carboxylic acid cake or saidcarboxylic acid cake with solvent to a vapor seal zone; and (e) addingat least one diol to said water-wet carboxylic acid cake in a carboxylicacid/diol mixing zone to form said carboxylic acid/diol mixture.
 35. Aprocess according to claim 34 wherein said carboxylic acid is selectedfrom a group consisting of terephthalic acid, isophthalic acid,naphthalene dicarboxylic acid, trimellitic acid and mixtures thereof.36. A process according to claim 34 or 35 wherein said diol is selectedfrom the group consisting of ethylene glycol, diethylene glycol,n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4butanediol, cyclohexanedimethanol, and mixtures thereof.
 37. A processaccording to claim 34 wherein said carboxylic acid/diol mixing zonecomprises at least one device selected from the group consisting of anagitated vessel, a static mixer, a screw conveyor, and a PETesterification reactor.
 38. A process according to claim 34 wherein saidcarboxylic acid is terephthalic acid and said diol is ethylene glycol.39. A process for producing a terephthalic acid/diol mixture, saidprocess comprising: (a) removing in a solid-liquid separation zoneimpurities from a terephthalic acid slurry to form a slurry or caketerephthalic acid product and a mother liquor stream; (b) adding solventin a solvent wash zone to said slurry or cake terephthalic acid productto produce a terephthalic acid cake with solvent and a solvent motherliquor stream; (c) optionally, adding water in a water wash zone to saidterephthalic acid cake with solvent to produce a water-wet terephthalicacid cake and a solvent/water by product liquor stream; (d) routing saidwater-wet terephthalic acid cake or said carboxylic acid cake withsolvent to a vapor seal zone; and (e) adding at least one diol to saidwater-wet terephthalic acid cake in a carboxylic acid/diol mixing zoneto form said terephthalic acid/diol mixture.
 40. A process according toclaim 39 wherein said solvent wash zone comprises a solid-liquidseparation device that is operated at a temperature between about 40° C.to about 155° C.
 41. A process according to claim 40 wherein said waterwash zone comprises a solid-liquid separation device that is operated ata temperature between about 40° C. to about 155° C.
 42. A processaccording to claim 39 or 40 wherein said adding occurs at a temperaturebetween about 40° C. and about 290° C.
 43. A process according to claim39 wherein said diol is selected from the group consisting of ethyleneglycol, diethylene glycol, n-butylene glycol, i-butylene glycol,n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixturesthereof.
 44. A process according to claim 39 wherein said diol isethylene glycol.
 45. A process according to claim 39 wherein saidcarboxylic acid/diol mixing zone comprises a device selected from thegroup consisting of an agitated vessel, a static mixer, a screwconveyor, and a PET esterification reactor.
 46. A process according toclaim 34 or 39 wherein said solvent is added counter current to the flowof said slurry or cake carboxylic acid product.
 47. A process accordingto claim 34 or 39 wherein said water is added counter current to theflow of said carboxylic acid cake with solvent.
 48. A process accordingto claim 46 wherein said water is added counter current to the flow ofsaid carboxylic acid cake with solvent.
 49. A process according to claim48 wherein said water wash zone comprises from about 2 to about 4 stagesof water counter current washes.
 50. A process according to claim 46wherein said solvent wash zone comprises from about 2 to about 4 stagesof solvent counter current washes.
 51. A process according to claim 47wherein said water wash zone comprises from about 2 to about 4 stages ofwater counter current washes.